One of astronomy's long held myths about star formation debunked

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Washington, August 28 (ANI): An international team of researchers has debunked one of astronomy's long held beliefs about how stars are formed.

Since the 1950s, astronomers have thought that in a family of new-born stars, the ratio of massive stars to lighter ones was always pretty much the same.

"This was a really useful idea. Unfortunately it seems not to be true," said team research leader Dr Gerhardt Meurer of Johns Hopkins University in Baltimore.

The different numbers of stars of different masses at birth is called the 'initial mass function' (IMF).

By measuring the amount of light from a population of stars, and making some corrections for the stars' ages, astronomers can use the IMF to estimate the total mass of that population of stars.

Results for different galaxies can be compared only if the IMF is the same everywhere, but Dr Meurer's team has shown that this ratio of high-mass to low-mass newborn stars differs between galaxies.

To arrive at this finding, Dr Meurer's team used galaxies from the HIPASS Survey (HI Parkes All Sky Survey) done with CSIRO's Parkes radio telescope.

The astronomers measured two tracers of star formation, ultraviolet and H-alpha emissions, in 103 galaxies using NASA's GALEX satellite and the 1.5-m CTIO optical telescope in Chile.

"All of these galaxies were detected with the Parkes telescope because they contain substantial amounts of neutral hydrogen gas, the raw material for forming stars, and this emits radio waves," said CSIRO's Dr Baerbel Koribalski, a member of Dr Meurer's team.

The astronomers measured two tracers of star formation, ultraviolet and H-alpha emissions, in 103 galaxies using NASA's GALEX satellite and the 1.5-m CTIO optical telescope in Chile.

Meurer's team found that the ratio of H-alpha to UV emission, varied from galaxy to galaxy, implying that the IMF also did, at least at its upper end.

Dr Meurer's team suggests the IMF seems to be sensitive to the physical conditions of the star-forming region, particularly gas pressure.

For instance, massive stars are most likely to form in high-pressure environments such as tightly bound star clusters.

The team's results allow a better understanding of other recently observed phenomena that have been puzzling astronomers, such as variation of the ratio of H-alpha to ultraviolet light as a function of radius within some galaxies.

This now makes sense as the stellar mix varying as the pressure drops with radius.

Importantly, the team also found that essentially all galaxies rich in neutral hydrogen seem to form stars.

"That means surveys for neutral hydrogen with radio telescopes will find star-forming galaxies of all kinds," Dr Meurer said. (ANI)

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